1. Field of the Invention
The present invention relates to digital video processing.
2. Description of the Related Art
In U.S. Pat. No. 5,450,500 and UK Patent Application 9407155.2 there is disclosed a digital colour processor (DCP) for colour correction in which only pixels that are specifically selected to be modified are processed by the digital circuitry. The pixels that are not to be modified are passed through the DCP without any processing that could create rounding or other errors. The processor comprises:
input means for receiving a stream of digital pixel data representative of pixels in a video picture; PA1 selecting means for testing digital pixel data in said stream and selecting said data for modification if and only if it meets predetermined selection criteria; PA1 modifying means for modifying said selected pixel data according to predetermined modification parameters to generate modified data; PA1 first combining means for combining said modified data from said modifying means with unmodified data from said input means to generate output data; and PA1 output means for supplying said output data to further equipment. PA1 In contrast, in a conventional architecture, all of the pixels in the picture would be processed through the same signal modification path, possibly being converted from red, green and blue (RGB) to hue, saturation and luminance (HSL), and then back again to RGB, causing errors.
An advantage of the above system is that pixels to be modified can be selected not just in accordance with colour parameters but in accordance with other parameters such as position. Thus, only pixels within a certain area might be modified.
Pixel selection advantageously is carried out by using the architecture referred to below as the "pixel identification table" or alternatively as the "cache tag RAM". The pixel identification table stores digital bits which define which pixels will be selected from the pixel stream for modification. Pixels may be selected as a function of their color (hue) as in prior systems, and/or as a function of other criteria, such as saturation, luminance, (X,Y) pixel coordinates, sharpness, and texture, alone or in any combination.
Further, after a pixel or region to be changed has been isolated, other parameters besides (H,S,L) color attributes can be changed. For example, the sharpness or even the (X,Y) coordinates of a region can be changed. Modifying the (x,y) coordinates of a region would be useful, for example, for special effects such as moving an object in the picture. Detecting pixels according to their (X,Y) coordinates could also be useful for copying pixels at a given x,y from one frame to another for scratch concealment. The latter process might be carried out simply by, for the given X,Y, controlling the frame store of the DCP (discussed below), so that those specific pixels are not overwritten from frame to frame.